Various types of pressure cylinders which are longitudinally slit have been proposed; a piston is longitudinally slidably retained within the cylinder, and a flexible sealing strip is provided, sealing the slit in the region between the piston and an end cap of the cylinder, so the pressurized fluid admitted to the cylinder will be retained therein, moving the piston, the sealing strip peeling off from the slit, or reseating itself on the slit, as the piston moves.
In accordance with a previously provided structure, the piston has a web element attached thereto, passing through the slit which, in turn, is connected to a bail-like structure which engages in guide grooves or guide rail elements located parallel to the longitudinal slit at the outside wall of the cylinder, to guide the motion and power transmitting web-shaped element. The guide tracks preferably are located on both sides of the slit, are parallel to each other, and provide longitudinal tracks for the motion transmitting element to retain it in position and to provide for easy sliding movement thereof.
U.S. Ser. No. 383,795, filed June 1, 1982, Kaiser, assigned to the assignee of the present application, to which German Patent Disclosure Document No. DE-OS 31 24 915 corresponds describes such an arrangement in which the motion transmitting element is supported on a pair of guide tracks or guide rails. The motion transmitting element is capable of accepting transverse forces or torques, since further torque transmission to the piston within the element itself is inhibited by engagement of the guide elements on the bail and the tracks.
It has been found, in use, that high internal pressures and unusual torques may tend to distort the cylinder and/or the guide tracks and/or the bail elements, resulting in difficulties in operation thereof, and possibly even in malfunction.
Guiding the motion transfer element requires engagement of the guide elements on the bail--which reaches around, and in some embodiments may at least partly encompass the cylinder--with some play or clearance since, otherwise, easy sliding motion is inhibited. Providing or permitting some play or clearance also permits a small, limited tilting movement of the motion transmitting element with respect to the axis of the cylinder. It has been found that, upon heavy loading, the motion transmitting element and/or the web thereof may be subjected to elastic deformation. The flexible sealing strip which extends longitudinally of the cylinder to seal the longitudinal slit thereof is lifted off sealing engagement from the slit in the region of the motion transmitting element. Consequently, some axial minimum distance must be provided between the sealing rings and the lifting-off range, which requires a certain minimum distance for the length of the pistons within the cylinder. Upon twisting or tipping torques being applied to the motion transmitting element, the length of the pistons within the cylinder have a lever effect, which may result is substantial radial deflection of the ends of the pistons. Piston rings or other sealing elements which are secured thereto must accept deflecting forces which, upon frequent occurrence, leads to difficulties with sealing, premature damage or possible destruction thereof. Additionally, such deflection results in non-uniform loading of the sealing rings or piston rings, which further detracts from long useful life and ready sliding movement thereof within the cylinder structure.
Motion transfer elements of the type in which a longitudinal slit is provided have the particular advantage that the cylinders can be made quite long, with respect to their diameter. If the cylinders are long, they may tend to bow downwardly, or deflect, for example due to their own weight; if hydraulic fluid is used, introducing the fluid within the cylinder changes the weight-distance relationship of the static loading of the cylinder which, additionally, contributes to unexpected deviation from predetermined dimensions or positions.